1. Field of the Invention
The present invention relates to the upgrading of hydrocarbon oils and, more particularly, relates to an improved process for removing metallic contaminants from petroleum feeds, especially high boiling fractions.
2. Discussion of the Prior Art
The adverse effects of nickel, vanadium and other metallic contaminants found in petroleum fractions boiling above about 950.degree. F. upon catalysts employed in petroleum processing operations and upon combustion equipment in which such high boiling fractions are used as fuels have long been recognized. In catalytic cracking operations, for example, very small concentrations of such contaminants in the feed to the cracking unit lead to the rapid poisoning of the catalyst, causing a significant decrease in the yield of cracked products, an increase in the production of coke and gases and a marked shortening of the catalyst life. Metallic contaminants present in residual fuels have similarly deleterious effects in that they (1) attack the refractories used to line boilers and combustion chambers, (2) cause slagging and deposits on boiler tubes, combustion chamber walls and blades of gas turbines and (3) severely corrode high temperature metallic surfaces with which they come in contact.
Much research has been devoted to the problem of developing methods for removing metallic contaminants from high boiling petroleum fractions in order to overcome these difficulties. Exemplary of such work are U.S. Pat. No. 3,203,892 and 3,245,902, which disclose demetallization of high boiling petroleum fractions by treating the contaminated fraction with hydrofluoric acid in the liquid phase.
Various oxidizing agents have also been employed in treating crude oil to remove vanadium complexed with porphyrins; see ACS Division of Petroleum Chemistry, Volume 18, pages 645-647 (1973). Among the oxidizing agents disclosed are Cl.sub.2, SO.sub.2 Cl.sub.2, N.sub.2 O.sub.4, t-butyl hydroperoxide and benzoyl peroxide. However, chlorine-containing reagents result in incorporation of chlorine in the feed, which renders the feed more corrosive and hence less processable. The remaining reagents disclosed are not as effective in reducing vanadium content as are the chlorine-containing reagents, which typically reduce the vanadium content to about one-half the original value.